Zig-zag sewing machine



20, 1968 BUNSAKU TAKETOMI 3,369,510

ZIG-ZAG SEWING MACHINE Filed Sept. 13, 1965 v 2 Sheets-Sheet 1 FIG. I

22 I l/22b I2 6b 7b 7a 60 l f I} I/ I/ I 16 38 l|87c2l7 42 J 40 INVENTOR.

BY BuNsaKu TRKETOM 1968 BUNSAKU TAKETOMI 3,369,510

ZIG-ZAG SEWING MACHINE 2 Sheets-Sheet 2 Filed Sept. 13, 1965 FIG.3'

FIG. 4

FIG.5

R. O T N E V W BY Bunsmm THKETOMI fl medium tts free

3,369,510 ZIG-ZAG SEWING MACHINE Bunsaku Taketomi, 9 2-chome, Uchijama-cho Chikusa-ku, Nagoya-shi, Aichi-ken, Japan Filed Sept. 13, 1965, Ser. No. 486,817 Claims priority, application Japan, Nov. 22, 1964, 39/ 65,742 Claims. (Cl. 112158) ABSTRACT OF THE DISCLOSURE A zig-zag sewing machine wherein the needle bar describes two kinds of zig-zag motions. The machine is provided with a changeover mechanism which selects the desired motion, i.e., straight zig-Zag or V-shaped stitches. The cam follower is of a particular construction and the movement of the cam is indirectly transmitted to the follower.

This invention relates to zig-Zag sewing machines of the type in which the needle bar can make two kinds of zig-Zag stitching motions, and, more particularly, to a changeover mechanism for such sewing machines which can selectively change the mode of stitching operations from one to another.

A main object of the invention is to provide a novel changeover mechanism for two-mode zig-Zag sewing machines of the above type, in which change-over from one mode to another mode of operations can be easily and reliably carried out.

- Another object of the invention is to provide a twomode zig-zag sewing machine which can produce V- shaped stitches of thread as well as ordinary straight zigzag stitches.

The above and other objects of the invention will be apparent from the following detailed description taken in connection with the attached drawings in which like parts are designated by like reference numerals and characters, and in which:

FIG. 1 is a plan view of the zigzag sewing machine according to the invention, with the top cover removed;

FIG. 2 is a front elevation, partly in section, of the sewing machine according to the invention, with the top cover removed,

FIG. 3 is a perspective view illustrating the needle bar carrying frame and change-over mechanism of the machine shown in FIGS. 1 and 2,

FIG. 4 shows examples of patterns produced by the machine, and

FIG. 5 is a perspective view of a throat plate which may be used with the sewing machine according to the invention.

Referring now to the drawings, the sewing machine shown has a structure comprising a hollow casing C fixed on a base B, the casing C including a vertical hollow pedestal S and a horizontal hollow arm A.

On the extreme end of the arm A a pair of vertically opposed supports 22 is provided through which pivot pins 20 extend to rotatably support a generally U-shaped frame 21 having a pair of upper and lower extensions 19. As best shown in FIG. 3, the frame 21 is thus rotatable about a vertical pivot axis to permit swinging movement of the extensions 19. Through the free end of these extensions 19, there extends vertically a pair of vertically opposed pivot pins 42 which also rotatably support a U- shaped needle bar frame 18 having a pair of upper and lower extensions 17. These upper and lower extensions 17 are also swingable about a vertical axis.

A needle holding bar 16 vertically extends through the free ends of the extensions 17 of the frame 18. The

needle bar 16 is passed at the lower portion thereof through a sleeve 17,, formed integrally with the lower extension 17 and at the upper portion thereof through an enlarged end 27 of a connecting lever 27 and tightly through a sleeve 15 positioned on the end 27,. Thus, it will readily be understood that the needle bar 16 is freely displaceable both longitudinally and transversely with respect to the horizontal hollow arm A due to the provision of two vertical pivot axes 22-22 and 4242.

About the vertical extension of the U-shaped frame 18, there is provided a coil spring 45 which is fixed at one end thereof to the vertical extension of the U-shaped frame 21 and in engagement with the lower extension 17 at the other end thereof in a manner to urge the extensions 17 to swing counter-clockwise (as viewed from above) about the vertical axis 4242.

As clearly shown in FIG. 3, the upper support 22 has a guide plate portion integral therewith, the guide plate portion having a straight guide edge 22 extending longitudinally of the horizontal hollow arm A. The straight guide edge 22,, serves to guide therealong the sleeve 15 of the needle bar 16. Since the extensions 17 and, therefore, the sleeve 15 are always urged against the guide edge 22 by a spring 45, the sleeve 15 and, therefore, the needle bar 16 are oscillated along a longitudinally extending straight line without transverse displacements to perform an ordinary straight zig-zag stitching operation when driven through the connecting lever 27.

On the guide plate portion of the upper support 22, there is provided a guide plate 14 which is transversely dis laceable along the upper surface of the guide plate portion as shown by the double-headed arrow in FIG. 3. The guide plate 14 is slidably received at theside edges thereof in groove 22 cut in the support 22 and has a substantially V-shaped concave guide edge 14,, facing the upper sleeve 15. The sliding movement of the guide plate 14 is effected by a mechanism which will hereinafter' be described. V

When the guide plate 14 is caused to slide toward the sleeve 15 beyond the front guide edge 22,, of the plate portion, and the sleeve 15 and, therefore, the needle bar 16 are driven through the connecting lever 27, the sleeve 15 and, therefore, the needle bar 16 are oscillated along a V-shaped path with the sleeve 15 being urged against the V-shaped guide edge 14,. Thus, it will be apparent that when the needle bar 16 is driven in such a manner that it hops in two steps from one end to center of the face 14, and from center to the other end of the face, patterns having stitches of threads extending obliquely to each other, for example, as shown in FIG. 4 may be ob- I tained.

The zig-zag movement producing mechanism and change-over mechanism will now be described in detail. Referring now to FIGS. 1 and 2, particularly, a main driving shaft 35 journalled within the casing C has a worm 1 in mesh with a worm wheel 2, the reduction ratio being selected to be 4:1. The worm wheel 2 has a pair of zigzag movement producing cams 3 and 4 which are located above the wheel and co-axially secured on the shaft of the wheel. It will be apparent that the cams 3 and v4 make l/4 revolution during one revolution of the main shaft 35.

The upper cam 3 is used for producing the two step movement of the needle bar 16 and has therearound four lobes positioned at equal angular intervals with one lobe having the largest radius, a diametrically opposite lobe having the smallest radius, and the remaining two lobes having an intermediate radius between said largest and smallest radii. The lower cam 4 is used for producing the ordinary step movement of the needle bar 16 and has therearound four lobes positioned at equal angular intervals with two opposite lobes having a larger radius and the other two opposite lobes having a smaller radius.

In conventional zig-zag sewing machines, the motion of such a cam as the cam 4 is directly transmitted to a cam follower which in turn transmits its movement to the needle bar through a suitable mechanism.

According to an important feature of this invention, however, the movement of the cam 3 or 4 is indirectly transmitted to a cam follower, which is in the form of an arcuate swing arm 23 pivoted at one end, through a roller 6 or 7, respectively. These rollers 6 and 7 are carried on the free ends of links 6 and 7 respectively. The upper link 6, is at the base end thereof pivoted to one end of a bell-crank lever 6 which is at its central angular portion pivotally mounted by a vertical pivot pin 12 carried on a support 11 provided on the inner wall of the casing C. The other end of the bellcrank lever 6 is bifurcated as shown at 6 The lower link 7 is also at the base end thereof pivoted to the free end of one arm of a T-sliaped lever 7 which is at its central portion pivotally mounted by the vertical pivotpin 12, co-axially with and below the bell-crank lever 6 The free end of the other arm of the T-shaped lever 7 is bifurcated at 7 The bifurcated end 7,, receives therein a pin 13 secured on the guide plate 14. The free end of the leg of the T -shaped lever 7 is also bifurcated as shown at 7 The bifurcated ends 6,, and 7 of the levers 6 and 7,, receive therein triangular cams 9 and 8, respectively. The triangular cams 8 and 9 are pivotally carried by a cam shaft 16 at their apex portions and in oppositely extending relationship with regard to the shaft 10. The cam shaft .10 has projecting therefrom a handle 51 for manually rotating the shaft.

By shifting the handle 41 leftward (as viewed in FIG.

1), the cam shaft 10 is rotated clockwise, which clockwise rotation causes the bell-crank lever 6 to rotate clockwise to the position shown in FIG. 1, while causing the T-shaped lever 7 to rotate counterclockwise to the position shown in FIG. 1. In this position, the roller 6 carried on the free end of the upper link 6 is caused to enter the space between the cam 3 and the arcuate swing arm 23, while the roller 7 carried on the free end of the lower link 7 is caused to move out of the space between the cam 4 and the arcuate swing arm 23. As the T- shaped lever 7 is rotated anticlockwisely to the position shown, its bifurcated end 7,, in engagement with the pin 13 causes the slidable guide plate 14 to advance beyond the guide edge 22 into the position of FIG. 1.

By shifting the handle 41 rightward, the cam shaft 10 is rotated counterclockwise. This counterclockwise rotation of the shaft 10 causes the bell-crank lever 6 -to rotate counterclockwise, while causing the T-shaped lever 7 to rotate clockwise. In this position, the roller 6 is retracted from the space between the cam 3 and the swing arm 23, and the roller 7 is advanced into the space between the cam 4 and the swing arm 23. On the other hand. the guide plate 14 is retracted to the position shown in FIG. 3.

The swing arm 23 functions as a cam follower as hereinbefore mentioned. This swing arm 23 is of arcuate form as shown and pivoted at one end thereof to a portion of the casing C by a vertical pin 40. The swing arm 23 has on the convex side thereof a roller engaging face 23,, adjacent the free end.

A rocker lever 25 is pivoted at its base end to a portion of the casing C by a vertical rod 36 and has the free end thereof connected to one end of a compression coil spring 30, the other end of which is secured to the inner wall of the casing C. To the intermediate portion of the rocker lever 25, there is pivotally connected a connecting arm 26 by a pivot pin 31. The connecting arm 26 has a roller 24 carried on the free end thereof.

Thus, it will be apparent that the rocker lever 25 is always urged, by the action of the spring 30, toward the 4. swing arm 23, thereby forcing the roller 24 against the concave side of the swing arm 23 through the connecting arm 26 and that the swing arm 23 is always forced to press the roller 6 or 7 against the peripheral face of the cam 3 or 4, respectively. The pivot pin 31 also serves to pivotally connect the connecting link 27 to the inter mediate portion of the rocker lever 25. As previously described, the connecting link 27 is connected at 27 to the needle bar frame extension 17.

The needle amplitude, control means may comprise a generally L-shaped lever 28 pivoted by means of a pin 29 and having one end 28 thereof engaging the connecting arm 26 and the other end 33 thereof projecting from the casing C for manual operation. The lever 28 may have rigidly secured therewith a profiling cam follower 32 which follows a profiling cam 34.

In operation, the mainshaft 35 is suitably rotatedand this rotation is converted through a crank mechanism 38 into reciprocating movements of the needle bar 16-as is well known in the art. On the other hand, the cams 3 and 4 are driven by the main shaft 35 through the worm 1 and worm wheel2. If the handle 41 is in the leftwardly shifted position with all of the components in the positions as shown in FIG. 1, therotation of the cam 3 will cause swinging movement ofthe swing arm 23, through the roller 6 interposed between the cam 3 and arm 23, theswinging movement being effected in a manner determined by the contour of the cam 3. This swinging movement of the arm 23 is in turn transmitted through the connecting arm 26 to the rocker lever 25. The swinging or oscillating movement of the rocker lever 25 is in turn transmitted to the needle rod 16 through the connecting link 27. It will be apparent that the manner in which the needle bar 16 oscillates is similar to the manner of oscillation of the swing arm 23.

As hereinbefore described, the cam 3 has a lobe of maximum radius, a lobe of minimum radius radially oppositely arranged to the first mentioned lobe, and a pair of radially oppositely arranged lobes of intermediate radius. When the maximum radius lobe is brought in engagement with the roller. 6, the needle bar 16 assumes the rightmost position (as viewed in FIG. 1). When an intermediate radius lobe is brought into engagement with e the roller 6, the needle bar 16 takes the middle position in which it is located at the vertex of the V-shaped edge 14,, of the guide plate 14 advanced to its operative position, the needle bar 16 being. forced against the guide edge 14,, by the spring 45.

When the succeeding minimum radius lobe comes inposition. The maximum radius lobe comes next to the roller 6, and the needle bar 16 returns to its original rightmost position. While the needle bar 16 is going through a cycle as above described, the main shaft 35 makes four revolutions because of thereduction rate of the worm and worm wheel gearing, thereby permitting four axial reciprocating movements of the needle rods. It is thus apparent that four stitches of thread are formed along the guide edge 14 for one revolution of the cam 3.

The length of stitches or amplitude of the needle bar 16 may be modified by shifting the end 33 of the lever 28 so as to change the position of roller 24 along the swing arm 23.

When straight zig-zag sewing operation is required, the handle 41 is shifted to the right position. In this position, the bell-crank lever 6 is rotated counterclockwise to the position in Which the roller 6 is retracted from between the cam 3 and arm 23, and the T-shaped lever 7 is rotated clockwise to the position'in which the roller 7 advances between the cam 4 and swing arm 23, and the guide plate 14 is retracted to inoperative position. Thus, when the. .main shaft 35 is driven, the cam 4 acts upon the roller 7 to cause the swinging movement of the arm 23, which movement causes the longitudinal oscillation of the needle bar 16.

As hereinbefore described, the cam 4 has a pair of diametrically opposed lobes of larger radius and another pair of diametrically opposed lobes of smaller diameter. When one of the larger radius lobes comes in contact with the roller 7, the needle bar 16 is moved to its rightmost position (as viewed in FIG. 1). When an adjacent smaller radius lobe comes in contact With the roller 7, the needle bar 16 is moved to its leftmost position. When the succeeding larger radius lobe comes in contact with the bar 16 as the cam rotates, the needle bar 16 returns to its original rightmost position. The movement of the needle bar 16 is the same for the remaining half revolution of the cam 4.

Thus, it is apparent that in this straight zig-zag stitching position the needle bar undergoes two reciprocating movements along the straight guide edge 22 now placed in operative state, for one revolution of the main shaft 35.

In both modes of operation as above described, the shuttle designated by the numeral 37 is also oscillated in confronting relationship to the needle carried by the needle bar 16 through known mechanism actuated by the pivot shaft 36.

According to this invention, change-over between two modes of operation of the machine can be easily carried out by merely shifting the handle 41, and the advancing and retracting movement of the links 6 and 7 1. can be smoothly carried out because of the provision of the rollers 6 and 7. These rollers 6 and 7 assure a smooth trans mission of motion from cams 3 and 4 to the swing arm 23.

While a preferred embodiment of this invention has been shown and described hereinabove, it is to be understood that the invention may be modified or changed within the spirit or scope of the invention as set forth in the appended claims.

What I claim is:

1. A zig-Zag sewing machine, comprising a needle bar, means for carrying said needle bar in a manner to allow axial reciprocations thereof and to allow free displacements of the same in all directions normal to the axis of said needle bar, shuttle means adapted to cooperate with said needle bar and to move in registry with the latter, a main drive shaft for causing the axial reciprocations of said needle bar, a pair of cams adapted to be driven by said drive shaft, cam follower means adapted to be acted upon by either of said cams to make oscillating motions in a manner determined by the contour of either of said cams, means for transmitting the oscillating motions of said cam follower means to said needle bar to cause oscillations of the latter normal to the axis thereof, a pair of guide means adapted to be selectively made operative for guiding said needle bar as the bar oscillates, one of said guide means having straight means for permitting straight oscillations of the needle bar, the other of said guide means having V-shaped means for permitting V-shaped oscillations of the bar, and change-over means for selectively causing one of the cams to act upon said cam follower means and at the same time said one of the guide means to become operative for guiding said needle bar, or said other of the cams to act upon said cam follower means and at the same time said other guide means to become operative, said one of the cams having a contour adapted to cause the needle bar to traverse said straight means in one step during half a cycle of the oscillation of the bar thereby producing straight lateral stitching, and said other of the cams having a contour adapted to cause the needle bar to traverse said V-shaped means in two steps during half a cycle of the oscillation of the bar thereby producing V-shaped lateral stitching.

2. A Zig-zag sewing machine, comprising: a needle bar; means for carrying said needle bar including a first member pivoted at one side thereof for swinging movements about a vertical axis and a second member pivoted at one side thereof to another side of said first member for swinging movements about a vertical axis with regard to said first member, said second member having means at another side thereof for carrying said needle bar in a manner to allow vertical reciprocations thereof; shuttle means adapted to cooperate with said needle bar and to move in registry with the latter; a main drive shaft for causing vertical reciprocations of said needle bars; a pair of cams adapted to be driven by said drive shaft; cam follower means adapted to be acted upon by either of said cams to undergo oscillating motions in a manner determined by the contour of the cam so acting thereupon; means for transmitting the oscillating motions of said cam follower to said needle bar to cause oscillations of the latter normal to the axis thereof; a pair of guide plates adapted to be selectively placed in operative state for guiding said needle bar as the bar oscillates, one of said guide plates having a straight guide edge for permitting straight oscillations of the needle bar, and the other of said guide plates having a V-shaped concave guide edge for permitting V-shaped oscillations of the bar; means for urging the needle bar against the guide edges of said guide plates; and changeover means for selectively causing one of the cams to act upon said cam follower means and at the same time said one of the guide plates to be placed in its operative state, or the other of the cams to act upon said cam follower means and at the same time said other guide plate to be placed in its operative state, said one of the cams having a contour adapted to cause the needle bar to traverse said straight guide edge in one step during half a cycle of the oscillation of the bar thereby producing straight lateral stitching, and said other of the cams having a contour adapted to cause the needle bar to traverse said V-shaped concave guide edge in two steps along said V-shaped concave guide edge during half a cycle of the oscillation of the bar thereby producing V- shaped lateral stitching,

3. A zig-zag sewing machine, comprising a needle bar, means for carrying said needle bar in a manner to allow axial reciprocations thereof and to allow free displacement of the same in all directions normal to the axis of said needle bar, shuttle means adapted to cooperate with said needle bar and to move in registry with the latter, a main drive shaft for causing axial reciprocations of said needle bar, a pair of co-axial cams adapted to be driven by said drive shaft through a reduction gearing, the reduction ratio being 4:1, one of the cams having a pair of diametrically opposed lobes of larger radius and a pair of diametrically opposed lobes of smaller radius with said two pairs of lobes in angularly equally spaced relationship; the other of the cams having a lobe of largest radius, a lobe of smallest radius diametrically opposed in relation to said largest radius lobe, and a pair of diametrically opposed lobes of intermediate radius with said four lobes in angularly equally spaced relationship, cam follower means adapted to be acted upon by either of said cams to undergo oscillating motions in a manner determined by the contour of the cam so acting thereupon, means for transmitting the oscillating motions of said cam follower means to said needle bar to cause oscillations of the latter normal to the axis thereof, a pair of guide means adapted to be selectively placed in operative state for guiding said needle bar as the bar oscillates, one of said guide means having straight means for permitting straight oscillations of the needle bar, and the other of said guide means having V-shaped means for permitting V-shaped oscillations of the bar, and change-over means for selectively causing said one of the cams to act upon said cam follower means and at the sametime said one of the guide means to be placed in its operative state, or said other of the cams to act upon said cam follower means and at the same time said other guide means to be placed in its operative state, said one cam causing,

through said cam follower means and said transmitting means, the needle bar to undergo one oscillating cycle along said straight means during two axial reciprocations of the needle bar, and said other cam causing, through said cam follower means and said transmitting means, the needle bar to undergo one oscillating cycle along the V-shaped path during four axial reciprocations of the bar in a manner to move in two steps along the V-shaped path for half a cycle of the oscillation.

4. A zig-zag sewing machine, comprising a needle bar, means for carrying said needle bar in a manner to allow axial reciprocations thereof and to allow free displacements of the same in all the directions normal to the axis of said bar, shuttle means adapted to cooperate with said needle bar and to move in registry with the latter, a main drive shaft for causing axial reciprocations of said needle bar, a pair of cams adapted to bedriven by said drive shaft, cam follower means adapted to be acted upon by either of said cams to undergo oscillating motions in a manner determined by the contour of the cam so acting thereupon, means forcing said cam follower means toward said cams, means for transmitting the oscillating motions of said cam follower means to said needle bar to cause oscillations of the latter, normal to the axis thereof, a pair of guide plates adapted to be selectively made operative for guiding said needle bar as the bar oscillates, one of said guide plates being a fixed plate having a straight guide edge, and the other of said guide plates being a slidable plate disposed along said fixed plate and having a V-shaped concave guide edge adapted to be projected beyond and retracted from said straight guide edge, means for forcing said needle bar against said guide edges, a first lever pivoted for rotation and having connected to one end thereof a link which carries on its free end a first roller adjacent said cams and cam follower, a second lever pivoted for rotation at its central portion coaxially with said first lever and having connected to one end thereof a link which carries on its free end a second roller adjacent said cams and cam follower, said second lever being connected to said slidable guide plate at the other end thereof, and means for simultaneously rotating said pivoted levers in opposite directions to each other, the actuation of the last mentioned means to one position causing said first roller to advance between one of said cams and said cam follower and said second roller to retract from between the other of said cams and said cam follower so that said one of the cams actuates the cam follower, said actuation to one position simultaneously causing said slidable guide plate to retract from its operative position so as to make said straight guide edge operative, the actuation of the last mentioned means to another position causing said first roller to retract from between said one of the cams and said cam follower and said second roller to advance betweensaid other of the cams and said cam follower so that said other cam actuates the cam follower, said actuation to the other position simultaneously causing said slidable guide plate to project to its operative position, said one of the cams having a contour adapted to cause the needle bar to traverse said fixed guide plate straight edge in one step during half a cycle of the oscillation of the needle bar to produce straight lateral stitching, said other of the cams having a contour adapted to cause the needle bar to traverse said slidable guide plate V-shaped edge in two steps during half a cycle of the oscillation of the bar to produce V-shaped lateral stitching.

5. A zig-zag sewing machine, comprising: a needle bar; means for carrying said needle bar including a first member pivoted at one side thereof for swinging movements about a vertical axis and a second member pivoted at one side thereof to another side of said first member for swinging movement about a vertical axis with regard to said first member, said second member having at another side thereof means for carrying said needlebar in a manner to allow vertical reciprocations; shuttle means adapted to cooperate with said needle bar and to move in registry with the latter; a main drive shaft for causing vertical reciprocations of said needle bar; a pair of coaxial cams adapted to be driven by said shaft through a reduction gearing; the reduction ratio being 4:1; one of the cams having a pair of diametrically opposed lobes of larger radius and a pair of diametrically opposed lobes of smaller radius with said four lobes in angularly equally spaced relationship; the other of the cams having a lobe of largest radius, a lobe of smallest radius diametrically opposed to said largest radius lobe, and a pair of dia-= metrically opposed lobes of intermediate radius with said four lobes in angularly equally spaced relationship; a cam follower mechanism adapted to be acted upon by either of the cams to undergo oscillating motions determined by said contour of the cam so acting thereupon; means for transmitting the oscillating motions of said cam follower mechanism to said needle bar to cause oscillations of the latter normal to the axis thereof; a pair of guide plates adapted to be, selectively placed in operative state for guiding said needle bar as the bar oscillates, one of said guide plates being a fixed plate having a straight guide edge, and the other of said guide plates being a slidable plate disposed along said fixed plate and having a V-shaped concave guide edge adapted to be projected beyond and retracted from said straight guide edge;

spring means for forcing said needle bar against said guide edges; a first lever pivoted for rotation and having connected to one end thereof a link which carries on its free end a first roller adjacent said earns; a second lever pivoted for rotation at its central portion coaxially with said first lever and having connected to one end thereof a link whichcarries on its free end a second roller adjacent said cams; said second lever being connected to said slidable guide plate at the other end thereof; and means for simultaneously rotating said pivoted levers in opposite directions to each other, the actuation of the last mentioned means to one position causing said first roller to advance between one of said cams andsaid cam follower and said second roller to retractfrom be tween the other of said cams and said cam follower so that said oneof the cams actuates the cam follower mechanism, said actuation to one position also causing said slidable guide plate to retract from its operative position so as to make said straight guide edge operative, the actuation of the last mentioned means to another position causing said first roller to retract from between said one of the cams and said cam follower and said second roller to advance between said other cam and said cam follower so that said other cam actuates the cam follower mechanism, said actuation to the other position also causing said slidable guide plate to project to its operative position, said one cam causing said needle bar to undergo one oscillating cycle while traversing said straight guide edge twice and making two axial recipro cations, and said other cam causing said bar to undergo one oscillating cycle while traversing said V-shaped guide edge twice and making four axial reciprocations, in a manner to move in two steps along said edge for half a cycle of the oscillations.

References Cited UNITED STATES PATENTS 2,216,096 9/1940 Card 112158 X 2,682,845 9/1954 Robert et a1. 112-158 2,986,107 5/1961 Eriksson 112-158 RICHARD J. SCANLAN, JR., Primary Examiner. 

